FIG. 1A shows a multipath hybrid nested Miller compensation amplifier 100 disclosed in FIG. 11 of an article by Eschauzier et al, entitled “A programmable 1.5 V CMOS class-AB operational amplifier with hybrid nested Miller compensation for 120 dB gain and 6 MHz UGF,” Solid-State Circuits, IEEE Journal of, Volume 29, Issue 12, Dec. 1994 Pages: 1497-1504. The amplifier 100 is a multistage amplifier, combining both forward nesting (C2) and backward nesting (C3) of inner Miller feedback inside the outer Miller compensation loop (C1). Both C2 and C3 are at the same nesting level, so the design equations are similar to the singly nested multipath Miller amplifier disclosed in an article by Eschauzier et al., entitled “A 100-MHz 100-dB operational amplifier with multipath nested Miller compensation structure,” Solid-State Circuits, IEEE Journal of Volume 27, Issue 12, December 1992 Pages: 1709-1717.
A problem with the amplifier 100 is that DC offsets in amplifier stage Gm1 adversely affect the output of the amplifier 100. As shown in FIG. 1B, choppers 112 and 114 can be placed at the input and output of Gm1 to attenuate such DC offsets. To facilitate chopping, the output of Gm1 is made differential, Gm2 is given a differential input, and the Miller compensation capacitor C1 is split into C1a and C1b. The resulting amplifier 101 of FIG. 1B is the same as the circuit shown in FIG. 7.1 of an Article by Huijsing entitled “Instrumentation Amplifier Developments” AACD 2008 Proceedings, 2008 Pages: 105-119. Referring to FIG. 1B, the chopper 112 at the input of Gm1 frequency shifts the input signal up to the chopping frequency. The chopper 114 at the output of Gm1 shifts the signal back to baseband, but DC offset and 1/f noise from Gm1 remain frequency shifted up to the chopping frequency.